Antisense RNA is an RNA having a nucleotide sequence complementary to mRNA. Specifically, it is an RNA read from an opposite strand of a DNA strand encoding a sense gene. Sense-antisense RNAs are capable of forming a double-strand and, for example, it is known that a double-stranded RNA is necessary for RNA interference, a double-stranded RNA is involved in the regulation of translation of a protein by a small RNA called microRNA and the like.
About 2,500 pairs of sense-antisense genes have been identified in mouse, which include many noncoding genes that do not encode proteins (non-patent reference 1). About half of the sense-antisense gene pairs is considered to be coding-noncoding gene pairs. Also in human, the presence of about 2,600 pairs of sense-antisense RNA pairs is suggested (non-patent reference 2). However, experimental verification relating to the structures and expressions thereof is limited.
One of the present inventors and their coworkers have so far developed an oligo DNA chip that distinguishes and analyzes 1947 pairs of sense gene and antisense gene identified in mouse, and comprehensively analyzed the expression of sense-antisense genes (non-patent reference 3). As a result, they have found that more than 90% of the sense-antisense genes are expressed in actual tissues, and that the expression thereof shows tissue specificity. It has also been found that various sizes of RNAs are transcribed from the sense-antisense gene locus, most of the RNAs lack the poly(A) chain and they tend to be accumulated in the nucleus. Furthermore, RNA without the poly(A) chain was also found by analysis of Arabidopsis, and such properties were found to be common to animals and plants.
Nevertheless, the physiological role of such noncoding antisense RNAs has not been elucidated at all.
Meanwhile, some carcinomas have been reported to involve genes whose expression changes cancer-specifically (cancer marker genes). However, no reports are available that the expression of endogenous antisense RNAs, particularly of noncoding ones, changes specifically in cancers or other diseases.    non-patent reference 1: Kiyosawa et al, Genome Res. 13: 1324-1334 (2003)    non-patent reference 2: Yelin et al, Nat. Biotechnol. 21: 379-386 (2003)    non-patent reference 3: Kiyosawa et al, Genome Research, 15: 463-474 (2005)